Broke crankshaft

opie

Newbie
Hi.
I have a question and hope that I can get pointed in the right direction. About 3 years ago I bought a 1966 Buick Wildcat with a 401, numbers are matching. I drove it the first summer and then parked it, it needed some work.
The oil pressure light would come on when the engine warms up, so I knew it needed a overhaul. Compression was right around 135 on all cylinders.
So a couple months ago I started a complete restoration on the car. This last week I got into the engine and was shocked to find that the crankshaft was broken right in front of the 2nd main bearing. The way it broke, the front cylinders were still working.
The block looks salvageable to me. I have not taken it to the machine shop yet though. It also appears that the 2nd and 4th main bearing caps may be cracked.
Is it possible to change out the crank and a few main bearing caps or would I need to get the flywheel and harmonic balancer with the new crank??
if so, any direction would be much appreciated, preferable on the west coast so shipping doesn't kill the project because im in AK.
 
The crankshaft can just be changed out. Although, while not necessary, I would recommend balancing the assembly. The main caps are another matter, you will need the block line honed after finding some replacement caps.
With both the crank and caps being damaged, if you can find another block with a crank, they are not uncommon, it may be the best place to start,
Look for telriv on this site (Members in the upper menu), he may be able to help you.
 
opie,

Don't know how much I will be able to help, BUT here goes. In ALL my years I have NEVER seen a crankshaft break on a "NailHead", even when racing with the same crank for 20 some odd years. Replacing the crank after magnafluxing saw some tell-tale signs of stress cracks that were visible so that crank was set aside for a STOCK rebuild when it deemed nec. As far as the main caps cracking, AGAIN I have NEVER seen ANY main caps crack. I even sent some main caps to a manufacturer some years ago to check the possibility of making main caps out of billet forged steel & was told it would be a waste of time as the strength of the caps was as good as they can be stock so we NEVER went ahead with that project. For the abuse we put these things threw I'm surprised we didn't have more issues than we had. AND this was during dyno testing that had the ole "Nail" spinning to 7100RPM's. We regulary shifted at 6200RPM's. Before the trans. was replaced which wouldn't let us shift above 550RPM's the tell-tale tach told us when a shift was missed, for various reasons, told us that the engine had been up too 8000 + RPM's. YES it pounded the rod bearings, BUT it NEVER gave us a problem to worry about.
Now getting past all that. IF you align bore (never align hone) because it brings the center line of the cam & crank closer together you now will have a FOREVER loose timing chain AND we have no option for a larger cam or crank gear or shorter timing chain to take up this extra slack. Now I know that the standard practice with other engines you may have those options availble, BUT like I said we have NO CHOICE.
IF the machinist is good he can align bore the engine & take as little as possible off the block to the point that there will be a barely visable line where the boring bar didn't remove ALL of the material from the block. In this case I would not take ANY chances I would replace ALL the main caps & VERY CAREFULLY check ALL the main bolts.
I have caps, some bolts & a crank for a TH400 trans. IF you can't find anything. ANOTHER NOTE, you could use a crank from a '59 to '63 for a DynaFlow trans. ALL you would need is an adapter to mate to the TH400 trans. which I also have in stock.
Getting past ALL of the above next would be to sonic test the block to check for cylinder wall thickness. This is done in 3 spots, N-E-S-W for a total of 12 spots on each cylinder. From about '61-'62 it was a known fact that the tooling & castings were getting long in the tooth, so to say, & since the newer designed engines were coming out soon, 1967, there was nothing done to improve the situation so CORESHIFT was a huge problem. Because of the weight of the reciprocating assembly cylinder wall thickness needs to be as close to .150" wall thickness. When new MANY were not this thick to begin with. The reason for sonic testing. There are ways around this IF the engine gets this far.
One last thing. For the availibility of using GOOD rings we will not be doing a standard overbore like .020"-.030"-.040" etc.
A 401 has the possibility of using up to 5-6 different popular bore sizes for pistons & rings. I worked with a manufacturer for two years designing FORGED pistons for our "Nails" in the popular oversizes.

Hope I may have been some help.

Tom T.
 
Thank you for the info Bob and Tom.
I took a few photos of the crank. The 2nd main cap is definitely cracked. I will attach a photo.
If I manage to find caps and another crank, do i have it internally balanced or stay with the factory externally balanced system?
thank you Tom, I totally spaced out the trans part, ( too much other stuff on my mind at the moment). FYI the odometer on the car is at 73000 miles, so not that many miles in my book. it does appear that the timing cover had been removed at one point, why? I don't know. I am still trying to figure out why the crank broke. if you have any insight or want to see any parts of it just let me know. trying to figure why it happened.
i have another question about the heads. on the exhaust port of each cylinder is a external bolt/ plug. at first i thought it might be for fuel injection until i realized they go to the exhaust side of the cylinder. do u know what these are for??
Thank you for your help, it is very much appreciated.
I want to wish everyone a Merry Christmas
and happy holidays
 

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here is a photo of the bearing cap and the port on the heads.
 

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Those are California AIR (air injection reaction) heads from 1966. That was the last year of the nailhead and the first for this system for CA only. It pumped fresh air into the exhaust port to provide oxygen for the hot exhaust gas to ignite and burn completely.

It takes a hairline crack worked over time to fracture a crank. I imagine the cap damage was done after the crank broke and kept running. Usually they will run that way because they do not shear off straight and there is not enough clearance for the haves to pass one another. I'd pay close attention to the main webs too. The halves klunk and work on each other as it runs. It makes a horrible broken sound!

You will be best suited to an external balance unless you are going to run a high end race engine with a specialty crank built to be balanced that way. The Nailheads were all externally balanced engines and had the advantage of a forged crank from the factory.
 
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Thank you Dr. Frankenbuick.
it makes sense about the exhaust port because the car was manufactured out of the California plant.
im not planing on building a racer at the moment, just a cruzer with maybe a little suped up parts here and there.
thank you for the feedback, much appreciated.
 
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